1. Field of the Invention
This invention relates to an adhesive transfer method for transferring a toner image formed on a photosensitive material drum by an electrophotographic process to a transfer sheet provided with an adhesive surface, and an apparatus for carrying out the adhesive transfer method. This invention particularly relates to an adhesive transfer method for accurately carrying out the adhesive transfer and enabling simplification of the transfer mechanism, and an apparatus for carrying out the adhesive transfer method. This invention also relates to an image receiving web for adhesive transfer which is provided with transfer sheets and used for the adhesive transfer method and apparatus.
2. Description of the Prior Art
There have heretofore been known electric copying machines or electrophotographic printers for forming an electrostatic latent image on a uniformly charged photoconductor by projection of an original image thereonto or irradiation of a light beam modulated based on image signals thereonto, developing the electrostatic latent image into a toner image, and then transferring the toner image to a substrate formed of paper or the like.
On the other hand, various electrophotographic processes for recording a continuous tone image with good gradation reproducibility have heretofore been proposed. For example, in Japanese Patent Publication No. 48(1974)-38172, it has been proposed to employ an electrophotographic process wherein an electrostatic latent image formed on a photoconductor is developed into a toner image by use of a toner, an adhesive tape is then closely contacted with the toner image under pressure to peel off and pick up the toner image onto the adhesive tape, and thereafter the adhesive tape is adhered to a final substrate.
As to the method of transferring the toner image formed on the photoconductor onto a substrate such as paper, the method wherein the toner image is electrostatically transferred by use of a "corotron charger" has been widely used. However, this transfer method has the drawback that the transfer efficiency is low both at high density regions and at low density regions. On the other hand, with the adhesive transfer method wherein the toner image is transferred to the adhesive layer in the manner mentioned above, a very high transfer efficiency can be obtained regardless of the image density. Also from this viewpoint, the proposed electrophotographic process mentioned above is advantageous for the recording of a continuous tone image. FIG. 8 shows an example of the adhesive transfer apparatus for carrying out such an adhesive transfer method.
With the adhesive transfer apparatus shown in FIG. 8, a photosensitive material drum 110 provided with a photoconductor 111 disposed along the circumferential surface is rotated in the direction as indicated by the arrow A, and a toner image is formed on the circumferential surface by a toner image forming means 120 disposed around the photosensitive material drum 110. The toner image forming means 120 is provided with a charger 121, an exposure unit 122, a developing unit 123, a drum drying means 124, a discharger 125, and a cleaning roller 126, which are disposed in the direction of rotation of the photosensitive material drum 110. After the photosensitive material drum 110 is electrostatically given a uniform charge by the charger 121, an electrostatic latent image is formed on the photosensitive material drum 110 by exposure thereof to a light beam modulated in accordance with image information at the exposure unit 122, and is developed into a toner image by the developing unit 123. The toner image thus formed on the photosensitive material drum 110 is dried by the drum drying means 124, and is then transferred by adhesion at a position P1 onto a transparent, belt-shaped transfer sheet 101 which is provided with an adhesive surface and which is applied around a transfer roller 130. The transfer sheet 101 has been fed in the condition laid upon a belt-shaped, release agent coated paper 102 from a sheet feed roller 131, and is separated at a position grasped between nip rollers 132A and 132B from the release agent coated paper 102 which is wound up by a roller 133 for winding up the release agent coated paper. The transfer sheet thus separated from the release agent coated paper 102 is applied around the transfer roller 130 with the adhesive surface thereof facing out, and is moved at a speed equal to the rotation speed of the photosensitive material drum 110 in contact with the photosensitive material drum 110, whereby the toner image is transferred from the photosensitive material drum 110 to the transfer sheet 101.
The transfer sheet 101 onto which the toner image has been transferred is then passed between pressure adherence rollers 140A and 140B as a pair of nip rollers. On the other hand, a belt-shaped supporting sheet 103 formed of paper or the like is delivered from a supporting sheet feed roller 141 toward the pressure adherence rollers 140A and 140B. The supporting sheet 103 is passed between the pressure adherence rollers 140A and 140B together with the transfer sheet 101, and is thus adhered to the transfer sheet 101. The transparent transfer sheet 101 and the supporting sheet 103 adhered to each other are then cut by a cutter 142 in a unit of the image formation region.
However, with the adhesive transfer apparatus mentioned above wherein the belt-shaped transfer sheet 101 is applied around the transfer roller 130 and is passed between the pressure adherence rollers 140A and 140B, the transfer sheet 101 is slackened or pulled forcibly and the image transferred at the position P1 is cracked or distorted in cases where a difference arises between the operation speed of the photosensitive material drum 110 and the operation speeds of the pressure adherence rollers 140A and 140B in the course of the adhesive transfer. Also, at the time that the adhesive transfer is started at the position P1, it is necessary that the leading edge portion of the transfer sheet 101 be grasped between the pressure adherence rollers 140A and 140B. Therefore, no image can be transferred to the leading edge portion of the transfer sheet 101, and a part of the transfer sheet 101 cannot be utilized. Further, since the transfer sheet 101 is shaped in a belt form, it must be cut in a unit of the image formation region after being adhered to the supporting sheet 103. Accordingly, a cutting mechanism such as the cutter 142 must be provided, and the apparatus becomes complicated. Also, in cases where an adhesive material such as the transfer sheet 101 is cut, adhesive is apt to stick to the cutter 142, and troublesome maintenance for keeping the cutter 142 clean is required.